Muscular Strength, Endurance and Power(Resistance Exercises) Dr. Afaf A.M Shaheen Lecture 8 RHS 322

Outlines Strength, Endurance & Power Types of Skeletal Muscle Contraction Factors That Determine Levels of Strength, Endurance & Power Physiology of Strength Development Overload Principle Progressive Resistive Exercise (PRE) Resistance Training Techniques Used in Rehabilitation

Critical to maintain and improve in each area in order to achieve competitive fitness levels and return athlete to functional level following injury

Strength, Endurance & Power Muscular Strength Ability to generate force against some resistance Important to maintain normal levels for normal healthy living Imbalance or weakness can impair normal function Muscular Endurance Ability to perform repetitive muscular contractions against some resistance Power Ability to generate force quickly Combination of strength & speed Performance is limited without power

Types of Skeletal Muscle Contraction Isometric Contraction Contraction that produces m. tension but no change in m. length Concentric Contraction Contraction that causes m. shortening while tension increases to overcome some resistance Eccentric Contraction Resistance is greater than the muscular force being produced & muscle lengthens while producing tension

Types of Muscle Contraction

Force and Types of Muscle Contractions

Types of Skeletal Muscle Contraction Econcentric contraction Controlled concentric & eccentric contraction of same muscle over 2 separate joints Hamstring and rectus femoris of quadriceps Strength training must focus on functioning of muscle Multi-planar Various contractions - functionally

Factors That Determine Levels of Strength, Endurance & Power Size of Muscle Proportional to cross-sectional diameter of muscle fibers Increased cross-sectional area = increased strength and force production Hypertrophy Increase in muscle size Atrophy Decrease in muscle size

Factors That Determine Levels of Strength, Endurance & Power Number of Muscle Fibers Strength is a function of the number and diameter of muscle fibers Number of fibers is inherited characteristic

Factors That Determine Levels of Strength, Endurance & Power Neuromuscular Efficiency Strength is directly related to efficiency of the neuromuscular system Initial increases in strength during first 8-10 weeks are attributed to neuromuscular efficiency Efficiency enhanced strength in 3 ways Increase number of motor unit recruitment Increase in firing rate of each motor unit Enhance synchronization of motor unit firing

Factors That Determine Levels of Strength, Endurance & Power Age Men & women increase strength throughout puberty & adolescence Peaks at age 20-25 After age 25, max strength declines 1% annually Decline is related to physical activity Able to retard decline in performance through activity

Biomechanical Considerations Position of tendon attachment Relative position of tendon attachment to fulcrum of the joint The closer the tendon is to resistance, the greater the force produced Change in attachment will alter force generating capabilities Length-Tension Relationship Length of muscle determines tension that can be created Varying lengths will produce varying tensions Determined by overlap of actin-myosin filaments

Overtraining Imbalance between exercise and recovery Training exceeds physiological and psychological capacity of individual Can have negative effect on strength training May result in psychological or physiological breakdown Injury, illness, and fatigue can be indicators

Fast-Twitch vs. Slow Twitch Slow Twitch Fibers Type I or slow oxidative (SO) More resistant to fatigue Time required to generate force is greater in slow twitch fibers Primarily associated with long duration, AEROBIC activities Fast Twitch Fibers Type IIa (fast oxidative glycolytic- FOG) Moderately resistant to fatigue Type IIb (fast glycolytic - FG) Fatigues rapidly – true fast twitch Type IIx – fatigue resistant with force capacity (a<x<b) Produce quick, forceful contractions Short-term, high intensity activities, ANAEROBIC activities

Ratio in Muscle Both fiber types exist in individual muscles Ratio varies by muscle and by individual Postural muscles =  % primarily type I fibers Power, explosive strength muscles =  % type II fibers Genetically determined Large role in determining ability for a given sport activity Fiber changes due to training Enhanced metabolic capabilities through specific training

Physiology of Strength Development Muscle Hypertrophy – 3 theories Hyperplasia –  in number of muscle fibers Genetically determined & does not seem to increase with training Evidence exists of fibers splitting – conducted in animals Hypothesized increased number of capillaries – partially correct No new capillaries Increase in dormant capillary activity to meet needs of muscle

Physiology of Strength Development **Increased size and number of myofilaments Actin (thin) and Myosin (thick) When muscle is stimulated to contract, cross-bridges pull myofilaments closer which shortens the muscle, & produces movement at joint that muscle crosses Reversibility – adaptations of muscle due to training can begin to reverse within 48 hours of removing training

Other Physiological Adaptations to Resistance Exercise Strength of non-contractile structures Tendons and ligament increase Increased bone-mineral content Improved oxygen uptake If resistance training is high enough to elicit a cardiovascular response/adaptation Increased metabolic enzymes

Overload Principle To improve strength, muscle must be worked at a level higher than it is accustomed to Muscle will maintain strength if it is trained against a consistent resistance that it is accustomed to Existence of current strength & will result in increased muscle endurance Effective training requires a consistently increasing effort against progressively more resistant loads In rehabilitation, rate of progression is determined by athlete’s response to specific exercise Be mindful of pain when dealing with progression

Isometric Exercise Capable of increasing muscle strength at specific joint angles Exercise with no change in muscle length May produce spikes in systolic blood pressure Could cause life-threatening cardiovascular accident To reduce this event to occur - REMIND the person to breath Widely used in rehabilitation Attempt to use positional or functional exercise – work at multiple angles throughout the range if possible Contractions should be held for 10 seconds at frequency of 10 or more per hour Utilized to enhance lift or activity at “sticking point”

Progressive Resistive Exercise (PRE) Exercises that work through a full range of motion Isotonic or isodynamic contractions Most popular & commonly used technique Concentric vs. Eccentric Greater force can be generated due to lower number of motor units recruited allowing other motor units to be recruited to generate increased force Oxygen use is much lower with eccentrics Efficiency of eccentric exercise is higher than concentric exercise Needs of the body – acceleration and deceleration Must be able to control body movements – deceleration and eccentrics allows for this control

Free Weights vs. Exercise Machines Advantages & disadvantages for both Machines – Safety & easy to use Constraints on motion & generally single plane of motion Free weights – Do not restrict motion Incorporates certain level of neuromuscular control

Surgical Tubing (Theraband) or Exercise Band Allow for motion in multiple planes Ability to perform more functional movement Can be utilized with PNF & plyometrics Variable Resistance Change in force required at different angles to move a particular resistance Greatest when joint is at 90 degrees Accommodating resistance or variable resistance equipment changes resistance at different points in range

Progressive Resistive Exercise Techniques (PRE) Terminology Repetitions Repetition maximum (RM) Set Intensity Recovery period Frequency Recommended Techniques of Resistance Training Must consider 4 areas Amount of weight to be used Number of repetitions Number of sets Frequency of training

Multiple potential routines The healing process must dictate the program! Intensity is key Multiple potential routines Single set – 1 set 8-12 reps at a slow speed Tri-sets – 3 exercises for 1 muscle group, 2-4 sets with no rest Multiple sets – 2-3 warm-up sets with progressively increasing resistance followed by several sets at the same resistance Superset – multiple exercises, 1 set of 8-10 repetitions or 1 or 2 exercises, with multiple sets of 8-10 repetitions Pyramid – multiple sets decreasing repetitions and increasing resistance Split routine – Workouts exercise different groups of muscles on different days

Circuit Training Group of exercise (flexibility, callisthenic, strength, brief aerobic) Used to increase strength or endurance Move from one station to the next, performing exercise for a given time period or number of repetitions

Resistance Training Techniques Used in Rehabilitation DeLorme’s method Based on repetition maximum of 10 Designed for early rehab Designed for beginning rehab Introduced PRE – “progressive loading” Builds in warm-up period 50%, 75% and 100% of 10 RM Oxford method Used during early, intermediate & advanced levels of rehabilitation Percentages of 10 RM Diminishes resistance as muscle fatigues – “regressive load” 100%, 75%, 50% of 10 RM

Isokinetic Exercises Involves muscle contractions where length change of muscle is set at a constant velocity Maximal resistance throughout the range of motion Variety of machines/manufacturers are available Can be used with eccentrics & concentric exercise

Isokinetics as a Conditioning Tool Maximal effort for maximal strength gains Dynamometer will move at a set speed whether maximal or half of maximal effort is put forth Athlete can cheat with machine and not put forth the effort Not cost effective Isokinetics in Rehabilitation Gained popularity in rehabilitation during the 1980’s Provide objective means of athlete/patient evaluation Training at fast vs. slow speeds Functional speeds

Plyometric Exercise Encompass a rapid stretch of muscle eccentrically followed by a rapid concentric contraction to facilitate the development of explosive power Greater stretch relative to resting length = greater resistance muscle can overcome Speed of stretch is emphasized over magnitude Used to develop eccentric control of dynamic movements Exercises should be performed technically correct

Plyometric Exercise

Core Stabilization Strengthening Fundamental component of rehabilitation Strengthening of core (lumbo-pelvic complex) Used to Improve dynamic postural control Ensure appropriate muscular balance & joint movement about the core Improve neuromuscular efficiency and expression of dynamic functional movement Provide optimal stabilization of kinetic chain and balanced muscular functioning throughout the chain

Open vs. Closed Kinetic Chain Exercises Anatomical & functional relationships that exist in the upper and lower extremity Open kinetic chain May be needed when lower extremity is to be non- weight-bearing Closed kinetic chain Useful in rehabilitation Most activities call for weight bearing of foot or hand in some capacity May be more functional than open chain activities in some instances

Training for Muscular Strength vs. Muscular Endurance Strength and endurance are closely related As one improves, the tendency is for the other to do the same For strength development Heavier weight and low repetitions should be used Endurance training Lighter weight and high repetitions (10-15) are suggested

Resistance Training Differences Between Males & Females Females tend not to develop significant muscle bulk due to reduced levels of testosterone While bulk generally does not increase, muscle tone will increase through training in females Gains are primarily neuromuscularly related & tend to plateau for females

Strength/Body Weight Ratio Males tend to continue developing strength through increased bulk following the neuromuscular strength gains Strength/Body Weight Ratio Females tend to have a lower ratio due to higher levels of body fat Absolute strength differences Reduced when body size & composition are compared Leg strength can actually be stronger in females with upper extremity strength greater in males

Specific Resistive Exercises Used in Rehabilitation Goal of program To regain and possibly increase specific muscle strength Increase efficiency of movement Variety of exercise modes can be utilized to achieve goals

Isometric Exercise Used during initial stages of rehabilitation Useful when training through a full range of motion is contraindicated Serve to increase static strength, decrease atrophy, create muscle pump to reducing edema Progressive Resistive Exercise (PRE) Most commonly used strengthening technique Incorporates free weights, machines and tubing Utilizes isotonic contractions (concentric and eccentric contractions)

Isokinetic Exercise Incorporated in later stages of rehabilitation Uses fixed speeds with accommodating resistance Provides maximal resistance through full range of motion Commonly used as criteria for return of athlete to functional activity

Plyometric Exercise Generally incorporated in later stages of rehabilitation Relies on a quick eccentric stretch to facilitate a subsequent concentric contraction Encourages dynamic movements associated with power Due to the need to generate power in athletic activities, it is critical to incorporate it within a the rehabilitation process

Core Stabilization Essential for functional strength Core functions to dynamically stabilize the kinetic chain Core strength enables distal segments to function optimally and efficiently during force and power generation

Definitions of Some Terminology Repetition: number of times you repeat specific movement. Repetition Maximum (RM): maximum number of repetitions at a given weight. Intensity: the amount of weight or resistance lifted. Recovery Period: the rest interval between repetitions. 

References Kisner, C. & Colby, L. (2002). Therapeutic Exercise: Foundations & Techniques, 4th ed.